The present invention relates to a device comprising two articulated elements in a single plane, having means for controlling the disalignment angle of the two elements in relation to one another. One of these elements can be free to rotate around the longitudinal axis thereof, whatever the axis of the disalignment thereof in relation to the other element may be.
In the field of petroleum drilling, it is often necessary to use bent subs to deflect the drilling of the wells in a given direction while following a predetermined trajectory.
In order to have precise leading means which, at the same time, limit the time wasted handling the drill string, variable-angle bent subs adjustable from the surface are used.
In French patent A-2,432,079, a device is proposed which comprises two tubular elements assembled together, wherein the first element is rotatable around an axis forming an angle with the axis of the second element. The rotating of the first element with respect to the second element causes a disalignment of the two elements. The disalignment is maximum for a rotation through 180.degree. and cancels out for 360.degree..
But the principle of this device makes the first element describe the generatrices of a cone. This brings about great drawbacks as far as the adjusting time and the precision are concerned when the trajectory of the well is wanted to or has to be maintained along a plane. In fact, if the plane defined by the axis of the upper thread of the sub and the axis of the lower element is referred to, the orientation of this plane changes for each value of the disalignment angle. It is therefore necessary to restore at each adjusting of the bend the correct orientation of this plane in order to follow the planned trajectory.
Besides, this displacement principle causes twisting moments on the drill string.
U.S. Pat. No. 3,627,356 discloses an articulated bent sub in a plane whose angle variation notably occurs through the feeding of a stiff rod through the drill string.
This device cannot be used when the gravity is not active any longer, as it is the case with strongly inclined drillings. Moreover, the diameter of the inner passageway of the circulating fluids is noticeably decreased.
The prior art illustrated by these two patents describes no articulated device enabling a notation of one of the elements of the device around the axis thereof since, when a bent sub is used in a drill string, a downhole motor is necessarily inserted between the drill bit and the lower connection of the bent sub. This moves the bend away from the drill bit accordingly and considerably decreases the deflecting effect of such a string.